An optical transport network (OTN) technology serves as a core technology of a next-generation transport network, and includes technical specifications of two aspects: an electrical layer and an optical layer. For electrical layer technical specifications, currently, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) has defined an OTN as a 4×4080 structure. However, to satisfy upper-layer Internet Protocol (IP) service transport with continuously increasing traffic, an electrical layer technology corresponding to the OTN also needs to provide a matched variable-rate OTN. At present, the ITU-T is discussing to develop a new optical channel transport unit Cn (OTUCn) with a rate that exceeds 100 Gbit/s. A bit rate of the OTUCn is n times a reference rate. The reference rate is preferably 100 Gbit/s, n is variable, and C is the Roman number 100. With emergence of the OTUCn, a generic mapping procedure (GMP) is used to map a low order (LO) optical channel data unit (ODU) to the OTUCn, and a mapping granularity is fixed at a quantity of timeslots, of an optical channel payload unit (OPU) in the OTUCn, occupied by the LO ODU.
However, in this method, use of a fixed mapping granularity is not flexible enough, which may cause a problem that OTUCns that carry a same LO ODU but use different mapping granularities cannot interwork between a receive end and a transmit end.